The specific aim of this research is to study primary and secondary vestibular fibers ascending in the brain stem and projecting to specific parts of the cerebellum in the monkey and in the cat. It is planned to produce discrete lesions in the vestibular ganglia in the monkey and trace resulting degeneration in silver impregnated sections into the cerebellum. Injections of (H3) amino acids will be made into the ampulla of the semicircular canals and axoplasmic transport of the isotope will be studied in serial autoradiographs. The ascending secondary vestibular fibers in the brain stem and cerebellum will be determined by two methods: (1) discrete injection of (H3) amino acids into individual vestibular nuclei and autoradiography, and (2) injections of horseradish peroxidase (HRP) into (a) nuclei of the extraocular muscle, (b) accessory oculomotor nuclei, (c) thalamic relay nuclei and (d) fastigial nuclei and discrete regions of the cerebellar cortex - followed by study of the retro-grade transport of the enzyme in bright and dark field microscopy.